Image Use Policy

Most materials published on the Earth Observatory, including images,
are freely available for re-publication or re-use, including commercial
purposes, with the following exceptions:

    * where copyright is indicated, you must obtain the copyright
      holder’s permission; we usually provide links to the organization
      that holds the copyright,
    * images from the SeaWiFS sensor older than five years are in the
      public domain and can be re-used or re-published for any purpose. 
      Images less than five years old can be re-used only for
      educational or scientific purposes; any commercial use of such
      images must be coordinated with GeoEye.

We ask that NASA’s Earth Observatory be given credit for its original
materials; the only mandatory credit is NASA.

Source:

  http://earthobservatory.nasa.gov/ImageUse/